Mazda 6 Steering Wheel Controls

I want to go HU-less, and I want to keep my steering wheel controls. The buttons are VOL +, VOL -, Next track, Prev track, Mute, and Mode (changes from FM to AM to CD, etc).

Here is the wiring diagram for my HU harness:

The ones that are toward the middle, labeled "Steering" (green/white and red/black) are the wires that go to the steering wheel. I was thinking of cutting up an old USB gamepad, but I'm not sure if this would work since theres only 2 wires going to the HU.